Effects of Fentanyl-Midazolam Anesthesia for Cardiac Anesthesia on Bispectral Index and Awareness

Lee, Guie Yong; Han, Jong In

Abstract

Background: During cardiac surgery, patients are at risk of intraoperative awareness. We evaluated the Bispectral Index (BIS) to prevent awareness during fentanyl-midazolam anesthesia for cardiac surgery. In addition, the relationship between BIS and hemodynamic responses during precardiopulmonary bypass period was assessed.
Methods
Twenty-six patients aged 18-70 years undergoing cardiac surgery were studied. Anesthesia was induced with etomidate 0.3 mg/kg, fentanyl 5 microgram/kg and vecuronium 0.1 mg/kg. After a further bolus dose of fentanyl 200 microgram and midazolam 3 mg prior to the operation, maintenance infusion rates of fentanyl 1.5 microgram/ kg/h, midazolam 0.025 mg/kg/h and were continued throughout the surgery, with intermittent bolus doses depending on the hemodynamic responses. Isoflurane 0.5% was administered until the start of cardiopulmonary bypass. The BIS, mean arterial pressure and heart rate were recorded prior to anesthesia, induction, intubation, skin incision, sternotomy, aorta cannulation, 5 and 30 minutes after cooling, 5, 15, 30 and 45 minutes after rewarming, sternal closure and end of surgery. Patients were asked about intraoperative awareness on the second postoperative day.
Results
The mean BIS decreased from 95 prior to anesthesia to 41 postinduction and then remained below 50 throughout the surgery. BIS did not correlate with mean arterial pressure (r = 0.08) or heart rate (r = 0.02) during precardiopulmonary bypass period. No patient reported the recall of an intraoperative event.
Conclusions
Continuous infusion of fentanyl and midazolam with intermittent bolus doses during cardiac surgery maintain the BIS below 50 and are effective for preventing of intraoperative awareness. Hemodynamic responses are not related to BIS before the cardiopulmonary bypass.